1. Field of the Invention
The present invention relates generally to leak detection and, more particularly, to an apparatus and method for detecting leaks based on a volume of bubbles emitted from an object.
2. Description of Related Art
Numerous components are manufactured which must meet a standard for a "leak tightness". Leak tightness is a relative term, as nothing can ever be completely free of leakage. A balance must be made between the increasing cost of finding smaller and smaller leaks and their importance to the functioning of the component over its useful life. Leak tightness is the practical leakage that is acceptable under normal operating circumstances.
Components which require some degree of leak tightness, for example, include fuel tanks, radiators, fuel systems, water pumps, wheels, refrigeration systems, heater cores, torque convertors, hydraulic and pneumatic systems, etc. The acceptable leakage will depend upon the usage of the component with respect to the type of fluid which must be contained, i.e. a gas or a liquid, and whether or not the contents will be pressurized.
There are many devices available to test for the presence of a leak. One method is mass spectroscopy where a high vacuum is drawn around the component and a test gas (helium) is introduced into the component. A spectrometer is used to scan the vacuum space for the presence of helium. Another "test gas" leak detection method is described in U.S. Pat. No. 4,862,731, in which the vacuum exhaust is run past a test gas sensor. It is extremely difficult to quantify a leak using a test gas method of detection because of the difficulty in measuring the amount of trace gas emitted through the leak. Another method of leak detection is air pressure decay where a leak will reduce the vacuum in or surrounding the component tested. While this method does provide a measure of leak quantification, the air pressure decay is time consuming and not well suited for small leaks.
A long-used leak detection technology is the bubble detection method in which a component is submerged in a liquid such as water and bubbles emerging from the component indicate a leak. Improvements on this bubble detection method are shown in U.S. Pat. Nos. 3,590,256; 4,854,158; 4,924,694 and 4,903,524.
While these various devices can identify a "leak" by detecting the passage of one or more bubbles through a given area, and can even count the bubbles passing, none can accurately quantify the volume of the bubbles over time and thus the size of the leak.
Several leak quantifying apparatuses and methods are commonly used in industry. An example of one such leak quantifying apparatus and method is disclosed in U.S. Pat. No. 4,879,907 to Patterson et al. This patented apparatus is a soap film flowmeter which may be used to measure the flow rate of gas leaking from an object over a period of time. The patented flowmeter includes an inverted U-shaped gas flow tube adjustably mounted in a sensor assembly. The flowmeter measures the flow rate of the gas leak by admitting the gas into an inlet of the gas flow tube, introducing a soap film into the interior of the gas flow tube in a region adjacent the inlet, and permitting the entering gas to propel the soap film within the tube past a sensing region. The sensing region measures the elapsed time of the soap film past a pair of detectors and displays the result as a flow rate of the gas leak.
One problem of the above-patented flowmeter is that the flow rate of individual bubbles is measured to detect a leak. This is undesirable because the flow rate may vary between individual bubbles. Another problem of the patented flowmeter is that the volume of bubbles emitted from an object cannot be quantified. Yet another problem of the patented flowmeter is that a soap film is required to measure the flow rate of the gas leak. This is also undesirable because soap films are messy and must be continually supplied.